The present invention relates to polyurethane foams. Polyurethane foams have been very well accepted for many years because of their well known advantages and because of the wide variety of applications for which the foams can be used.
For example, rigid polyurethane foams are useful for producing insulative materials. It is often desirable to modify the properties of the rigid foams, for example to increase their flexibility in order to decrease cracking when a load is put on it.
Flexible and semi-flexible foams are commonly used, among other things, for furniture cushioning, for the fabrication of matresses and in many transportation means, for example for cushioning of seats. For these applications, it is often desirable to use flexible or semi-flexible polyurethane foams with high resilient and/or high load bearing properties.
Different suggestions have been made by those skilled in the art to modify the properties of polyurethane foams in the desired manner.
In U.S. Pat. No. 4,309,532 it is suggested to use a modified aminopolyol in preparing rigid polyurethane foams. The modified polyols are made by reacting a rigid foam polyol initiator having an active hydrogen functionality of at least 4 and an amine with one or more alkylene oxides to extend the polyol chain. An epoxy resin is added in such a manner that it is inserted at selected points along the length of the polyol chain or at the end of the resulting product. In U.S. Pat. No 4,373,034 is suggested use of a modified polyol for preparing flexible polyurethane foams with high load bearing properties. The modified polyols are made by reacting an initiator having an active hydrogen functionality of from 3 to 4 with one or more alkylene oxides to extend the polyol chain, and adding epoxy resin in such a manner that it is inserted at selected points internally along the length of the polyol chain. Unfortunately, the flexible foams have several disadvantages, e.g. the foams are not highly resilient and they are difficult to produce.
Accordingly, it would be desirable to provide polyurethane foams which have high flexibility, high resiliency and/or high load bearing ability.